Introduction
In a research, extraneous variables may cause an effect on the dependent variable. The purpose of a well-designed study is to ensure that the change in the independent variable does not arise from “extremity” (Campbell, 2007). Notably, researchers use various ways to ensure that the change in the independent variable is caused by the independent variable alone. Similarly, the researchers have a desire to carry out objective studies. Thus, unnecessary variations must be avoided.
Random assignment
In the case of subject variables, the effect on the dependent variable is controlled through random assignment. The common examples of subject variables include age and body weight (Campbell, 2007). Often, these variables are associated with individual differences between subjects regardless of their genetic resemblance. Random assignment of the subjects to go groups helps to distribute the result of subject variables. Researchers use random assignment as an important tool because it distributes uniformly the effects of variables uniformly across subjects. However, the researchers find it necessary to explicitly most variables before resorting to randomization.
Within-Subjects Design
Sometimes, control of variation due to extraneous variables is achieved through within-subjects designing of experiments. This method exposes all subjects to the conditions of the experiment. For simple designs that involve a single control and independent variable, then all subjects experience the control condition. In addition, each subject is exposed to experience the independent variable. When the variation between subjects is large, the within- subjects design becomes more effective (Campbell, 2007).
Matched-Sample Design
Additionally, it is possible to control variables by use of the matched-sample system. In this design, the variables are measured and then subjects and control for different variables matched. For example, a study involving effects of exercise to areas of the brain, subjects are arranged based on their initial ability. It is necessary to measure the differences in people’s mental abilities and then use a matched-in design. This method is effective in controlling the effects of extraneous variables especially when the sample size is small.
Conclusion
Control of extraneous variables is necessary in order to obtain valid experimental results. Therefore, to achieve the central objective of research, variations must be avoided to the irreducible minimum level.
References
Campbell, D. T., & Stanley, J. C. (2007). Experimental and Quasi-Experimental Designs for Research.
Controlling extraneous variables in experimental research: a research note. (2011). Accounting Education.
